Layer stack

ABSTRACT

The invention is directed to a layer stack for the acceptance of a liquid having a suction layer ( 1 ) with high absorbency sufficing for sucking up the liquid from the edge of the layer stack into its middle and having a first storage layer ( 2 ) with low absorbency that is not sufficient for sucking up the liquid from the edge of the layer stack up to its middle between which an intermediate layer ( 3 ) composed of non-absorbent material and adjoining the first storage layer ( 3 ) [sic] is arranged, whereby a non-absorbent edge layer ( 7 ) is arranged at that side of the first storage layer ( 2 ) facing away from the intermediate layer ( 3 ), and whereby the intermediate layer ( 3 ) comprises through holes ( 4 ) whose plurality, size and distribution is [sic] selected such that some of the liquid suctioned up by the suction layer ( 1 ) can proceed via the holes ( 4 ) to the first storage layer and thoroughly saturate this. By foregoing a second suction layer, electrolytic capacitors with a significantly lower space requirement can be manufactured.

[0001] The invention is directed to a layer stack for the acceptance ofa liquid having a suction layer, a storage layer and an intermediatelayer.

[0002] Layer stacks of the species initially cited are known fromelectrolytic capacitors whereby the intermediate layer is fashioned asanode layer, and whereby a respective suction and a storage layer arearranged at both sides of the intermediate layer. The two outermostlayers of the layer stack defined in this way are respectively coveredby a cathode foil. The suction or, respectively, storage layers aretypically implemented as paper layers, whereby the suction layer is apaper with low density (<0.6 g per cm³) and the storage layer is a paperhaving high density (>0.6 g per cm³). The paper layers are saturatedwith an electrolyte. They therefore serve, first, as storage medium forthe electrolyte. Second, the paper layers also have the job of limitingthe current of the mobile ions present in the electrolyte and thusachieving a high dielectric strength of the electrolytic capacitor. Theelectrolytic capacitors are typically manufactured by winding theabove-described layer stack onto a winding mandrel, as a result whereofa cylindrical body arises. Particularly given electrolytic capacitorswith high capacitance (>1 mF), cylinders having a length of a fewcentimeters thus arise. The electrolyte is introduced into the capacitorafter the winding of the capacitor. Due to the wound structure, theelectrolyte can only be supplied from the end faces of the woundcapacitor. Given electrolytic capacitors that exceed a specific length,the suction layer is required in order to transport the electrolyte fromthe end faces into the inside. Since the suction layer is a low-densitypaper and, corresponding great channels [sic], it is not suitable forachieving a high dielectric strength. The storage layer implemented ashigh-density paper is therefore additionally inserted between anode foiland cathode foil. The dense paper comprises channels with a smallcross-section and is thus extremely well suited for achieving a highdielectric strength. Due to its low absorbency, however, it does notsuffice as sole intermediate layer between cathode foil and anode foil.The various layers described given the known structure lead to a highvolume requirement of the electrolytic capacitor relative to itscapacitance. Particularly where electrolytic capacitors are to be builtinto miniaturized circuits, this is a considerable disadvantage.

[0003] An object of the present invention is therefore to offer a layerstack that, by foregoing one of the two suction layers, comprises alower volume requirement. This goal is inventively achieved by a layerstack according to claim 1. Advantageous developments of the inventionmay be derived from the further claims.

[0004] The invention recites a layer stack for the acceptance of aliquid that comprises a suction layer, a storage layer, an intermediatelayer and an edge layer. The suction layer has a high absorbencysufficing for sucking up the liquid from the edge of the layer stackinto its middle. The first storage layer has a low absorbency that isnot sufficient for sucking up the liquid from the edge of the layerstack up to its middle. An intermediate layer adjoining the storagelayer is arranged between the storage layer and the suction layer. Theintermediate layer is composed of a non-absorbent material and comprisesthrough holes. These holes connect the upper side of the intermediatelayer to its underside and are selected such in terms of plurality, sizeand distribution that some of the liquid suctioned up by the suctionlayer that is applied at the edge of the layer stack can proceed via theholes of the intermediate layers to the first storage layer andthoroughly saturate this. A non-absorbent edge layer is arranged at thatside of the first storage layer facing away from the intermediate layer.The storage layer is thus saturated with liquid exclusively via theholes in the intermediate layer.

[0005] The inventive layer stack has the advantage that a second suctionlayer arranged at the side of the storage layer can be foregone byutilizing the holes found in the immediate layer for saturating thestorage layer arranged at that side of the intermediate layer facingaway from the suction layer. As a result thereof, the volume requirementof the layer stack is reduced.

[0006] The inventive layer stack can be especially advantageouslyfashioned as electrolytic capacitor. To that end, a second storage layeris arranged at the side of the suction layer. Either the second storagelayer or the suction layer can thereby be adjacent at the intermediatelayer, since a good soaking of the first storage layer is achieved inboth instances. The edge layer is fashioned as first cathode layer. Asecond cathode layer is arranged at that side of the layer stack lyingopposite the edge layer. When an electrolyte, i.e., for example, anorganic liquid, wherein ions that conduct the electrical current arelocated is also employed, then the inventive layer stack can be employedas electrolytic capacitor. An electrolytic capacitor designed in thisway is especially space-saving due to the elimination of a secondsuction layer.

[0007] Paper layers are especially advantageously utilized as suctionor, respectively, storage layer. These paper layers are simultaneouslysuitable for the electrical insulation between anode layer and cathodelayer and for the limitation of the ion current. The ion current isinhibited all the more greatly the thicker the paper layer betweencathode layer and anode layer is. A paper having a density ρ₁<0.6 g percm³ is employed as suction layer. A paper having such a low densitycomprises a multitude of channels that can suck a liquid applied at theedge of the layer stack into the inside as a result of capillary action.A paper having a density ρ₂>0.6 g per cm³ is preferably employed asstorage layer. Papers having this high density comprise only smallchannels that are especially suited for limiting the ion current in theelectrolyte and, thus, for contributing to a high dielectric strength ofthe electrolytic capacitor.

[0008] Further, it is especially advantageous to employ a paper assuction layer wherein a line or wave structure is impressed. A paperprovided with a wave structure can, for example, look like a corrugatedsheet. As a result of the impressed lines or, respectively, waves, theabsorbency of the paper is enhanced, whereby the internal structure islargely preserved. A paper having a high density ρ₂>0.6 g per cm³ cantherefore be employed. Such a paper then has the advantage that, on theone hand, it is suited as suction layer and, on the other hand,comprises an enhanced dielectric strength, as a result whereof thethickness of the storage layer can be reduced.

[0009] Moreover, a layer stack is especially advantageous wherein thesuction layer and the second storage layer are the plies of a two-plypaper. Such a two-ply paper can, in particular, be advantageouslyemployed when the layer stack is wound on a winding mandrel. The two-plypaper has the advantage that it is does not tear as readily. Anelectrolytic capacitor manufactured of a layer stack wound onto awinding mandrel can be realized especially easily and quickly. Moreover,its capacitance can be very easily set by means of the plurality of theturns. The employment of a two-ply paper in band form for winding onto awinding mandrel is especially advantageous because only one band thenneed be supplied for the paper layer between anode foil and cathodefoil.

[0010] The invention is explained in greater detail below on the basisof exemplary embodiments and the Figures appertaining thereto.

[0011]FIG. 1 shows an inventive layer stack that is fashioned aselectrolytic capacitor in a schematic cross-section.

[0012]FIG. 2 shows an inventive suction layer having an impressed wavestructure.

[0013]FIG. 1 shows an inventive layer stack having an intermediate layer3 fashioned as anode. The anode is approximately 100 μm thick and iscomposed of [ . . . ] on both sides with approximately 0.2 through 1 μmthick oxidized aluminum. Particularly for the employment of high-voltageelectrolytic capacitors, holes 4 are etched into the intermediate layer3 that connect the two sides of the intermediate layer 3 to one another.The etching of the holes 4 occurs, for example, by means of electrolyticetching in HCl. The holes 4 that thereby arise have a diameter D between1 and 3 μm and are therefore suitable for the transport of a liquid fromthe upper side of the intermediate layer 3 to the underside of theintermediate layer 3. An edge layer 7 that is fashioned as first cathodelayer is arranged at the underside of the layer stack. Just like thesecond cathode layer 8 arranged at the upper edge of the layer stack, itis fashioned as a 20 through 30 μm thick aluminum foil that is coveredwith a thin aluminum oxide layer.

[0014] A respective storage layer 2, 5 is arranged at the edge layer 7or, respectively, at the second cathode layer 8. This storage layer iscomposed of paper having a density of approximately 0.8 g per cm³. Sucha paper can, for example, be manufactured of cellular material. Due toits density, it is suitable for lending the electrolytic capacitor ahigh dielectric strength. The two storage layers 2, 5 must be saturatedwith an electrolyte. Since an application of the electrolyte is onlypossible at the edge of the layer stack, the electrolyte must betransported into the inside of the layer stack by means of a suitable,further layer. A suction layer 1 is therefore arranged between thesecond storage layer 5 and the intermediate layer 3, said suction layer1, as indicated by arrows, transporting the electrolyte from the edge ofthe layer stack into its inside and thereby saturating the secondstorage layer 5 with electrolyte. By utilizing the holes 4 in theintermediate layer 3, the first storage layer 2 can also be saturatedwith electrolyte with the assistance of the suction layer 1 withouthaving to arrange a further suction layer at the underside of theintermediate layer 3. The suction layer is composed, for example, of apaper having a density of 0.4 g per cm³ and has a thickness of 55 μm. Itcan, for example, be fabricated of jute paper. The fiber spacings in ajute paper are so great that the paper is excellently suited for theabsorption of liquids. Since the suction layer 1 also delivers acontribution to the dielectric strength of the capacitor, the secondstorage layer 5 can be selected somewhat thinner at 40 μm than the firststorage layer 2 at 65 μm. Due to the omission of a second suction layerarranged under the intermediate layer 3, an electrolytic capacitor withhigh capacitance and low space requirement can be realized with theinventive layer stack.

[0015]FIG. 2 shows a suction layer 1 into which a wave structure 6 isimpressed. As a result of the impressed waves, the suction layer (1) hasan enhanced absorbency since the waves form a type of channel whereinfluid can be transported. Due to the increased absorbency, suctionlayers 1 fashioned in this way can also be fabricated of denser paperhaving a density between 55 and 70 g per cm³. Such a suction layer 1then has a higher dielectric strength, this leading thereto that thesecond storage layer 5 shown in FIG. 1 can be implemented thinner,whereby the corresponding space is eliminated.

[0016] The invention is not limited to the embodiments shown by way ofexample but is defined in its broadest form by claim 1. List ofReference Characters 1 suction layer 2 first storage layer 3intermediate layer 4 hole 5 second storage layer 6 wave structure 7 edgelayer 8 second cathode layer D hole diameter

1. Layer stack for the acceptance of a liquid having a suction layer (1)with high absorbency sufficing for sucking up the liquid from the edgeof the layer stack into its middle and having a first storage layer (2)with low absorbency that is not sufficient for sucking up the liquidfrom the edge of the layer stack up to its middle between which anintermediate layer (3) composed of non-absorbent material and adjoiningthe first storage layer (3) [sic] is arranged, whereby a non-absorbentedge layer (7) is arranged at that side of the first storage layer (2)facing away from the intermediate layer (3), and whereby theintermediate layer (3) comprises through holes (4) whose plurality, sizeand distribution is [sic] selected such that some of the liquidsuctioned up by the suction layer (1) can proceed via the holes (4) tothe first storage layer and thoroughly saturate this.
 2. Layer stackaccording to claim 1 that comprises a second storage layer (5) adjoiningthe suction layer (1).
 3. Layer stack according to claim 2, whereby thesecond storage layer (5) adjoins the intermediate layer (3).
 4. Layerstack according to claim 2, whereby the suction layer (1) adjoins theintermediate layer (3).
 5. Layer stack according to claim 1 through 4,whereby the suction layer (1) is a paper with a density ρ₁<0.6 g/cm³ andthe first or, respectively, second storage layer (5) is a paper with adensity ρ₂>0.6 g/cm³.
 6. Layer stack according to claim 1 through 5,whereby the suction layer (1) is a paper into which a line or wavestructure (6) is impressed for increasing the absorbency.
 7. Layer stackaccording to claim 5 through 6, whereby the suction layer (1) and thesecond storage layer (5) are the plies of a two-ply paper.
 8. Layerstack according to claim 1 through 7 that is wound onto a windingmandrel.
 9. Layer stack according to claim 1 through 8 that is anelectrolytic capacitor, whereby the edge layer (7) is a first cathodelayer, whereby a second cathode layer (8) adjoins that side of thesuction or, respectively, second storage layer (1, 5) facing away fromthe intermediate layer, whereby the intermediate layer (3) is fashionedas anode, and whereby the liquid is an electrolyte.
 10. Layer stackaccording to claim 9, whereby the intermediate layer (3) is an aluminumfoil covered with an approximately 0.5 μm thick aluminum oxide layer,and whereby the holes (4) are channels electrolytically etched into thealuminum foil with a diameter (D) between 1 μm and 3 μm.